9: Blood, Lymph, and the Immune System
- Page ID
- 100092
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- 9.1: The Fluid of Life- Introduction to Blood
- Blood is a specialized circulating connective tissue made up of plasma and formed elements: erythrocytes (red blood cells), leukocytes (white blood cells), and platelets. Together, these components allow blood to transport gases, nutrients, hormones, and wastes, defend against infection, regulate pH and temperature, and prevent blood loss through clotting, making it essential for maintaining homeostasis and sustaining life.
- 9.2: Hematocrit
- The hematocrit (Hct), or packed cell volume, measures the percentage of RBCs in whole blood and provides insight into the blood’s oxygen-carrying capacity. By spinning a blood sample in a centrifuge, the components separate into layers, allowing clinicians to compare the red cell layer to total blood volume and identify conditions such as anemia, dehydration, pregnancy-related dilution, or polycythemia based on whether the hematocrit is abnormally low or high.
- 9.3: Blood Plasma
- Blood plasma is the liquid portion of blood, composed of about 92% water and 7% proteins, and it serves as transport medium for nutrients, hormones, electrolytes, wastes, and dissolved gases. Its major proteins — albumin (maintains osmotic balance), globulins (transport and immune defense), and fibrinogen (clotting) — regulate fluid balance, immunity, and hemostasis, while serum is plasma without clotting factors.
- 9.4: Cells and Platelets of the Blood
- The formed elements of blood — erythrocytes, leukocytes, and platelets — are produced in red bone marrow and each have specialized roles: RBCs transport oxygen, WBCs defend against infection, and platelets enable clotting and tissue repair. A complete blood count (CBC) with differential evaluates the number, types, and appearance of these elements, providing important clues about conditions such as infection, anemia, immune disorders, or bone marrow dysfunction.
- 9.5: Erythrocytes — Tiny Oxygen Taxis
- The erythrocyte, commonly known as a red blood cell (or RBC), is by far the most common formed element. A single drop of blood contains millions of erythrocytes and just thousands of leukocytes. Specifically, males have about 5.4 million erythrocytes per microliter (µL) of blood, and females have approximately 4.8 million per µL. In fact, erythrocytes are estimated to make up about 25 percent of the total cells in the body.
- 9.6: RBC Life Cycle
- Erythropoiesis (production of RBCs) is a process stimulated by erythropoietin (EPO) released from the kidneys in response to low oxygen levels. After circulating for about 100–120 days, aging RBCs undergo eryptosis and are removed by macrophages, primarily in the spleen and liver, where hemoglobin is broken down, iron is recycled for new RBC production, and bilirubin is excreted in bile.
- 9.7: Aberrations from the Normal Blood Profile — Anemia vs. Polycythemia
- Anemia and polycythemia are disorders that disrupt the normal balance of RBCs and impair oxygen delivery. Anemia results from too few RBCs, decreased production, blood loss, or increased destruction, leading to fatigue, hypoxia, and potential organ strain, whereas polycythemia involves excess RBC production, thickened blood, and increased risk of clots, stroke, or heart attack.
- 9.8: Blood Doping
- Blood doping is the illegal and unethical practice of increasing RBCs or altering oxygen transport to enhance endurance by boosting oxygen delivery to muscles. Methods include blood transfusions, erythropoietin (EPO) and related drugs, HIF stabilizers, and synthetic oxygen carriers, but all carry significant health risks — such as blood clots, stroke, heart attack, and hypertension — and are monitored in sport through tools like the athlete biological passport and laboratory testing.
- 9.9: Hemostasis
- Hemostasis is the three-step process that stops bleeding: vascular spasm (vessel constriction), formation of a temporary platelet plug, and coagulation, in which a fibrin mesh stabilizes the plug to create a durable clot. Once the vessel is repaired, fibrinolysis dissolves the clot and anticoagulants help limit clot formation to restore normal blood flow.
- 9.10: Blood Clotting Disorders
- Blood clotting disorders occur when the hemostatic system becomes unbalanced, leading to either excessive bleeding or abnormal clot formation. Too little clotting can result from low platelet counts (thrombocytopenia) or missing clotting factors, as seen in X-linked hemophilia, while too much clotting may arise from excess platelets (thrombocytosis) or overactive clotting factors (thrombophilia), increasing the risk of deep vein thrombosis, stroke, or pulmonary embolism.
- 9.11: Overview of the Lymphatic and Immune Systems
- The lymphatic and immune systems work together to protect the body by maintaining fluid balance, filtering pathogens, and coordinating immune responses. Through a network of vessels, organs, and specialized cells, they detect and eliminate threats while supporting long-term immunity. These systems provide layered defenses, from rapid, nonspecific responses to highly targeted and memory-based protection.
- 9.12: Barrier Defenses and the Innate Immune System
- The innate immune system provides the body’s first and second lines of defense through mechanisms including physical and chemical barriers, immune cells, and inflammation, which act quickly to limit infection. These responses are rapid and nonspecific, helping detect and eliminate pathogens before they spread. Together, they form an essential early defense and help activate the more targeted adaptive immune response.
- 9.13: Key Concepts of Adaptive Immunity
- Adaptive immunity is a highly specific defense system that targets particular pathogens using B cells, T cells, and antibodies. Although it develops more slowly than innate immunity, it produces a powerful and precise response and creates long-lasting immunological memory. This memory allows the body to respond faster and more effectively to future infections.
- 9.14: Humoral Immune Response
- Humoral immunity is a branch of adaptive immunity in which B cells produce antibodies that circulate in the blood and lymph to target extracellular pathogens. These antibodies help neutralize toxins, tag pathogens for destruction, and form immune memory for faster responses upon re-exposure. This system provides a powerful and specific defense against infections outside of cells.
- 9.15: Cell-Mediated Immune Response
- Cell-mediated immunity is the second branch of adaptive immunity. It relies on T lymphocytes to recognize intracellular pathogens and abnormal cells, such as cancer cells. Cytotoxic T cells directly destroy infected or abnormal cells, while helper T cells coordinate the overall immune response, including the activation of B cells and cytotoxic T cells. This branch is especially important for eliminating intracellular infections, particularly those caused by viruses.
- 9.16: Immune Dysfunction and Clinical Connections
- Vaccines protect the body by preparing the immune system in advance. They are important for creating herd immunity in protecting both individuals and populations. Introduced are also some major immune dysfunctions, occuring when these defenses fail or misfire. Included are conditions such as immunodeficiency, autoimmune diseases, and allergic hypersensitivity.
- 9.17: Blood Types and Transfusions
- Blood typing and transfusion safety rely on antigen–antibody interactions that allow the immune system to distinguish self from non-self. The ABO and Rh systems determine compatibility based on specific red blood cell surface antigens and corresponding antibodies, making proper blood typing and cross-matching essential to prevent dangerous transfusion reactions such as agglutination, hemolysis, and shock.